This invention relates generally to apparatus for logging earth boreholes and specifically to methods and apparatus which utilize means in addition to, or which aid gravity in causing the well logging instruments to traverse the high angled earth boreholes.
It has become relatively common within the last few years to drill wells in the search for oil and gas and the like with a portion of the bore deviating from the usual vertical orientation thereof. The deviation or inclination may extend for a considerable distance at angles ranging to 70.degree., sometimes returning to the usual vertical orientation. In some instances, such boreholes may even extend past 90.degree. from the vertical and actually be extending in the up direction for some distance.
It is also well known in the art of drilling such wells to attempt the logging of the formations surrounding such boreholes with logging instruments run into the well bore on a wireline and/or a cable to perform various operations. Such tools usually depend upon the force of gravity to permit positioning of the well tool at the desired formation in the well bore.
Manifestly, the relatively horizontal angle of the deviated portion of the well bore will not permit the wireline actuated tools to move into the lower portion of the well bore since friction of the well tool in the deviated portion works against the force of gravity. Thus it has become essential to provide some means of causing the well logging instrument to pass through the deviated portions of the well bore.
Another problem associated with such boreholes relates to the instability of some formations penetrated by the well bore, thus causing borehole diameter changes, some very abrupt. Ledges are formed, and the logging instrument lodges against them.
It is therefore the primary object of the present invention to provide new and improved methods and apparatus for logging earth boreholes;
It is also an object of the present invention to provide methods and apparatus for logging deviated boreholes in which it is difficult for the well logging instrument to traverse the borehole.
The objects of the invention are accomplished, generally, by methods and apparatus which monitor the velocity of the logging cable at the earth's surface, which monitor the velocity of the well logging apparatus itself, and which activate additional means responsive to a comparison of the two velocities which facilitate the movement of the well logging instrument through the borehole.